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Description/Abstract

During mechanised forest harvesting, extraction routes may be armoured with a dense carpet of logging residues (slash roads) to reduce soil disturbance associated with heavy machinery. However, guidelines regarding the design of slash roads remain largely qualitative, and their efficacy as a means of ground protection uncertain. Trials were undertaken in north-east England and south-west Scotland to identify the main causes of slash road failure during repeated trafficking. Failure of the slash roads was defined as (a) deflection of logging residues and exposure of the ground surface to harvesting machinery or (b) mixing of logging residues with surface soils. The frequency of slash road failure was directly linked to terrain factors (soil water content, the presence of rocks, tree stumps, furrows and drain channels, or slope). In addition, failure was linked to the design of the slash roads where large diameter logging residues were readily deflected, or at junctions and turning points where 'shearing' of the slash road took place. A simple means of assessing the potential for slash road failure is presented based on terrain characteristics. These guidelines allow harvesting staff to locate extraction routes in order to maximise the structural longevity of the slash road, whilst reducing down-time associated with their repair. In addition, and where standard yield tables apply, a means of predicting the volume of logging residues available at any site is demonstrated, and the implications of this for effective slash road construction are discussed.